PHOENIX -- With the clock ticking down to Christmas, the United States Postal Service expected Monday to be the busiest mailing day of the year.

Millions of cards, letters and packages move through the mail processing facility in Phoenix every day, and that number rises during the holidays. Each night, hundreds of dedicated employees sort that avalanche of mail using automated equipment.

On Monday alone, employees expect to handle more than 600 million pieces of mail nationwide. Here in the Valley, teams will process some 10 million piece of mail. USPS hired some 200 temporary workers here in the Valley to help ensure your mail gets to its destination on time.

The Postal Service expects to deliver about 420 million packages during the holiday season, a 12 percent increase from last year. A similar increase is expected in Arizona.

In total, the Postal Service will deliver nearly 15 billion letters, cards, and packages from Thanksgiving to New Year's Eve.

If you have not done your mailing yet, you still have time to ensure your items are delivered on time. USPS says you need to keep the following deadlines in mind.